The invention relates to storage racks for storing nuclear fuel assemblies both during transport and during stationary storage. Preferably, the racks are highly overdamped, enabling them to best withstand vibrations caused by seismic events or rough handling.
Fuel for nuclear reactors is typically configured in the form of elongated fuel rods, which may be separate, stand-alone elements, or may be positioned within canisters. Hereinafter, the fuel rods and rod/canister combinations are referred to as fuel assemblies. Both before and following use, the fuel assemblies must be stored and/or transported with great care. To assure that such care is achieved, storage racks are often used to support a plurality of fuel assemblies in a generally parallel, spaced-apart configuration, while maintaining the fuel assemblies in a subcritical array environment. During storage, the racks and the fuel assemblies contained therein, may be completely submerged in a pool of water. The water provides cooling and additional shielding from nuclear radiation.
The fuel storage racks of the prior art typically consist of an assembly of hollow cells, each defined by an array of elongated rectangular cross-section boxes or compartments. The boxes are typically made by forming sheets of stainless steel into elongated rectangular cross-section tubes (typically 9 inches square by 14 feet long and welding the corners of the elongated tubes together to form a matrix of elongated hollow cells, each adapted the receive a single fuel assembly. Typically, the tubes are joined at their corners to common rod segments that are located at various positions along the adjacent corners of the tubes. Exemplary storage racks are disclosed in U.S. Pat. Nos. 4,695,424, 4,857,263, 4,948,553, and 4,366,115. Alternatively, the tubes can be held in place by support bars that are welded or otherwise affixed to the top and bottom ends of each tube such as disclosed in commonly owned U.S. Pat. No. 5,384,813 entitled Highly Damped Storage Rack for Nuclear Fuel Assemblies, which is hereby incorporated by reference.
A neutron absorbing (or "poison") material, such as borated stainless steel, is typically welded or otherwise rigidly affixed to each of the walls of the boxes to absorb neutron flux from the fuel assemblies which may be positioned within the boxes, thereby avoiding an undesirable concentration of neutrons. Alternatively, the neutron absorbing material can preloaded against the walls of the tube as described in commonly owned U.S. Pat. No. 5,384,813 in order provide a coulomb damping function for improved resistance to vibration damage.
One of the problems associated with assembling prior art storage racks is that the tolerance variation of the longitudinal bow for the tubes can vary up to .+-.0.1875 inches. After assembling the tubes together at their ends, any bow over the fourteen foot length of the tube makes it difficult to weld rod segments at positions intermediate to the ends. In addition, if the bow were to increase over time, the adjacent corners could bear against each other, potentially causing premature failure of the storage rack.
Accordingly, it is an object of the present invention to provide an improved storage and/or transport rack for nuclear fuel assemblies.
Another object of the present invention is to provide an improved storage rack for nuclear fuel assemblies which is highly overdamped to enable the rack to withstand the vibration of seismic events or rough handling such as may be encountered during transportation of the rack.
It is another object to provide a storage rack for nuclear fuel assemblies which has improved torsional and crush strength.
A further object is to provide an improved storage rack for nuclear fuel assemblies which may be easily and inexpensively manufactured.
It is yet another object to provide a storage rack for nuclear fuel assemblies which is resistant to failure due to the bowing of the tubes of the storage rack.
It is yet a further object to provide a storage rack for nuclear fuel assemblies which is resistant to failure due to the bowing of the individual cell tubes of the storage rack by providing support elements that are positioned between adjacent cell tubes of the storage rack in order to facilitate alignment of the cell tubes and resist bowing by biasing the support elements against adjacent cell tubes to distribute the forces attributable to bowing over the adjacent cells.
Other objects of the invention will in part be obvious and will in part appear hereinafter.